@Tetraspore: No, adding the three Tantalus members to the party is still relying on shared slots.
It is in the realm of possible to add slots to them, because it's in the engine source code (that can be modded using Albeoris's Memoria or other C# DLL editing tools like dnSpy). It however requires a big amount of work and it would be hard to deal with the interface (in the party selection menu and for the shop portraits).
The game is designed with 9 character slots ; a lot of datas and static numbers are relying on that, not to mention that the Field scripts are, as for them, expecting to have 8 team characters at some points (same problem with Beatrix).
I am not interested myself in adding Blank, Marcus or Cinna to the team of permanent characters, because I don't see the point both gameplay-wise and story-wise. But if I ever get into it, I'll let you know.
@ploppo: You're welcome

As ToraCarol said, you'll have the ability to recruit her. That means you must go to Alexandria's castle after getting the airship where you can meet her and let her come in the team. Then she'll appear in the party selection menu just like any other playable character.
@ToraCarol: no, sorry... As said, HW has little to no control over the cameras. I really don't know why the camera is scrambled for you and not for me (I mean, when you add Blank in your mod versus when I add Beatrix in mine).
I will release a new version of HW pretty soon (surely this week-end). I have investigated an "auto-translation" feature for translating texts automatically and, while I saw that it was possible, it would have delayed too much the next version (that has important bug fixes among other things).
So there will be an auto-translate in the future, but not in the upcoming version.